I'm a current USyd first year student planning to major in Psyc
there are about 5 courses in which you can do psyc at the uni, so you should choose which one to do which will allow you to also explore your other interests. The courses are listed here:
http://www.psych.su.oz.au/future_students/psychology_other_degrees.shtml
The basic thing you need to know is to be a practicing psychologist you have to do a 4th year of uni. At USyd that's in the form of an Honours degree, but at other uni's it can be just a 4th year of study. So basically, when undertaking a major in Psychology with the intent of becoming a psychologist, you need to be aiming to qualify for 4th year study.
The basic psychology degree is BPsychology, where you undertake a major ONLY in psychology, while also studying a few arts or science subjects (that's the 'arts stream' or 'science stream'). The great thing about that degree is it guarantees you a place in Honours, which is very competitive. However, you must maintain a distinction average or you basically get kicked out.... Let me tell you, a distinction average is HARD! So if you are fully committed to your work and think you can maintain top marks, then go for it!
I'm studying psychology through the BArts. It's pretty much the same as the BPsych, except I also have to major in an Arts subject. I'm majoring in History, but there are a billion other subjects you can do - I really like how flexible the degree is. In the BArts you do exactly the same psyc subjects as those doing BPsych. The only difference is your entry to Honours isn't guaranteed, so you have to fight for it. I'd say you'd probably need a Distinction average as well, but at least if you don't get that you don't get kicked out of the degree!
The other courses I don't know too much about, but they all do exactly the same psyc subjects whatever the degree, with different subjects you also have to study. Psyc is very popular at USyd, like someone above said, there are over 2,000 students in the first year courses. How hard it is to get into depends on what course you choose to study it in - I think the BPsyc ATAR was like 97.5, but the BArts ATAR was only 84. There are 3 lectures per week and 1 tutorial, so your full time hours will depend on what other subjects you do. This year in the BArts I only went to uni for 3 days per week hehe
. The only experience I've had with neuropsychology was a lecture series this year, and I found it interesting but challenging. You also need to be interested in anatomy because you have to learn all the parts of the brain, some parts of the body etc. You don't have to decide what psyc subjects to take until 2nd year anyway, so you'll get to experience it first.
Hope that helped